This invention relates to an apparatus for dispensing particulate matter. The apparatus includes a feeder, comprising a circular disk which dispenses particulate matter from a supply source. The invention has application in numerous areas where particulate matter is required to be dispensed in measured quantities and at precise rates.
The particular disclosure of this application is of an apparatus for dispensing and injecting sawdust into a kiln used for firing brick. A kiln generally comprises a long tunnel-like enclosure formed of refractory brick. While the details of commercial brick manufacture vary considerably, in the disclosure below individual bricks are molded and then placed in a pre-determined arrangement on small flatbed railway cars. The bricks are first dried in a dryer which uses waste heat from the kiln. The individual cars carrying the brick roll on railway tracks down the length of the kiln. Each time a new load of brick is rolled into the kiln, each car in front of it is moved further along the kiln. This process is called the "intermittent push" method and results in one car of fired brick exiting the kiln as each car of brick enters from the other end. Upon entering the kiln, the dried bricks are preheated to a temperature of approximately 500.degree. F. (260.degree. C.). The bricks then enter a furnace zone of the kiln where the heat gradually increases from approximately 1,400.degree. F. (760.degree. C.) to 2,000.degree. F. (1093.degree. C.). From the furnace zone of the kiln the ricks move into a cooling zone where the heat absorbed by the bricks is gradually dissipated. The waste heat from the cooling area is conveyed to the dryer.
The temperatures within the furnace zone of the kiln must be maintained within very close tolerances. Firing the bricks to a temperature even 25.degree. F. (14.degree. C.) lower than optimum can result in bricks being too soft and absorbent to meet building requirements. Conversly, firing the bricks at a temperature 25.degree. F. (14.degree. C.) higher than optimum can cause vitrification, whereby bricks turn into a glass-like substance with virtually no absorbency. For this reason, the temperatures within the kiln are very closely monitored. In order to maintain the temperature within very close tolerances, the amount of fuel being consumed within the kiln must be closely monitored and adjusted periodically. This is relatively easy to accomplish when the kiln is heated with liquid or gaseous fuel, such as diesel fuel or natural gas. However, because of the substantial price increases in petroleum and natural gas in recent years, the use of these fuels has, in most cases, become economically impractical. For this reason more and more kilns are being converted to burn sawdust or some other non-petroleum fuel. In areas of the United States having large lumber or furniture manufacturing industries sawdust can be purchased as a waste product at inexpensive prices, making it a highly economical fuel. For example, approximately 600 lbs. (272 kg.) of sawdust has the equivalent B.T.U. (Kg.-cal.) output of 45 gallons (170 liters) of diesel fuel or 5,000 cubic feet (142 cubic meters) of natural gas. At a typical price of $30.00 per short ton (0.85 metric tons) of sawdust delivered to the kiln, the economic advantages of sawdust as a fuel are apparent.
However, the physical characteristics of sawdust have caused substantial problems in using it as a kiln fuel where precise control of the feed rate is essential to maintaining the kiln temperature within required tolerances. As mentioned above, sawdust is often purchased by brick manufacturers from lumber yards or furniture factories where the sawdust is generated as a waste product. The physical characteristics of the sawdust may vary substantially depending on the process by which it was produced, the type of wood and its moisture content. Soft woods produce a fuzzy sawdust which tends to stick together in clumps. Other sawdust may contain long curls or strings of wood as well as wood chips and splinters.
Several prior art devices for feeding sawdust into a kiln are currently in use. One type of feeder uses a vibrating feed hopper which "sifts" sawdust onto a moving conveyor. The sawdust falls off the edge of the conveyor into one of a plurality of longitudinally aligned funnels. Each of the funnels feeds a separated injector which injects the sawdust into the kiln. However, these vibrating dispensers cannot increase or decrease the sawdust feed rate in a linear manner except within a very limited range. Below a certain level of vibration the sawdust ceases feeding properly. Above a certian level of vibration the rate of flow increases at far above a linear rate. Furthermore, no means are provided by which some injectors can be delivered greater quantities of sawdust than others. This makes it virtually impossible to compensate for temperature variations which may exist from one side of the kiln to the other.
Another system uses individual vibrators, each of which feeds a separate funnel. Individual feed rate control is therefore possible, however, the feed rates are still non-linear.
Another prior art feed system uses a "distributor" principle, whereby a central dispensing arm rotates and successively feeds from six to ten radially extending feed arms. Each feed arm dispenses the sawdust into a funnel and then into an injector. In this system, no individual control or continuous feeding is possible.
Yet another system is based on fertilizer feeder principle, much like those used on farms to fertilize crop acreage. Adjustable slot-type openings are provided in the bottom of a longitudinally extending funnel-shaed hopper. A rod having agitator blades extends down the length of the hopper just above the bottom openings and rotates, dispensing sawdust through the openings. Individual adjustment from one opening to the next is impossible, as is intermittent feeding.
An analysis of the above prior art systems and their respective deficiencies demonstrates that an ideal solid fuel feeding system should have three capabilities: First, the ability for a linear increase and decrease in feed rates across an extremely wide range; Second, individual feed control should be provided for each feed unit, since a conventional brick kiln has a very large number of separate fuel injector locations, each potentially requiring a slightly different feed rate; and, third, the system should be quickly and easily adjustable.